1. Field of the Invention
The present invention relates to a conveying system and, more particularly, to a conveying system in which a substrate is conveyed while rotating.
2. Description the Related Art
There are occasions where substrates supported by the conveying carriage are desired to be rotated on the conveying carriage in order to perform a predetermined series of operations. For example, U.S. Pat. No. 4,874,639 (corresponding to Japanese Patent Laid-open (kokai) Publication No. 178,871/1988) discloses the technology involving a substrate as works with a paint in a film thickness exceeding the thickness which causes sagging, unless otherwise treated in the coating step, and rotating the coating substrate about approximately horizontal line in parallel to the axis of the coating substrate in the drying step prior to the time when the paint starts sagging until the paint is cured to such an extent that it does not cause sagging. The range of the rotating speeds of the substrate in this case is from the speed at which the substrate is rotated so as to change the position of the substrate upon which gravity acts prior to causing sagging due to gravity to the speed at which no sags are caused due to centrifugal force.
This patent discloses the technology of rotating the substrate loaded on the conveying carriage by utilizing the relative speed difference between the main and auxiliary conveyors. The main conveyor is provided for conveying the carriage and an auxiliary conveyor is disposed along the main conveyor.
It is desired, however, that the substrate loaded on the conveying carriage be suspended in the predetermined position for the following step, when the rotation of the works is not needed any more. For instance, when an automotive vehicle body is to be coated while rotating, it is desired that the body be suspended in its upright position for an assembly step which follows after drying of the paint.
From this point of view, it is considered that the conveying carriage is provided with a mechanism for suspending the works in the predetermined upright position when the carriage has reached the point of time when the coating of the works has been finished and no rotation of the works is needed any longer. At this end, such a mechanism includes, for example, a locking mechanism for locking the rotation of the works in a predetermined position, means for detecting the position in which the works are rotated, operation means for operating the locking mechanism when the works have reached the predetermined position and auxiliary driving means for rotating the works in the predetermined position. Since a number of instruments are provided on the conveying carriage, the carriage becomes so large in size and expensive that it is disadvantageous to have a number of such expensive carriages disposed in the coating station of an assembly line. Further, coating of the works using such carriages requires a large surplus of energy particularly in drying the coat in a drying oven in order to heat and maintain the works at the predetermined temperatures.